The standard intelligence quotients and indexes of the Wechsler Intelligence Scale for Children-Third Edition (WISC-III) are computed using equal weights, giving each subtest equal psychometric influence on each composite score. This computational method is recommended in the WISC-III manual primarily due to practical reasons, notably the simplicity of calculation procedures. Alternatively, calculating the composite scores by differential weighting of the composite subtests offers more psychometric precision and inferred accuracy, and may result in more meaningful scores at the individual diagnostic level. The goal of this study was to compare the WISC-III index scores of a common clinical group using standard computational model (equal weights) with the differentially weighted model derived from the seminal Reliable Components Analysis (RCA) of the WISC-III (Parker a Atkinson, 1994). Results clearly indicate that the differentially weighted subtest model provides clinicians a useful alternate way to understand a child's intellectual repertoire using WISC-III profiles. In this sample of relatively low functioning children, their intellectual achievement assessment was somewhat better and more adaptive using the differentially weighted model than the equally weighted model. There was considerable divergence between the models at the individual qualitative classification level.This computational method is recommended in the WISC-III manual primarily due to practical reasons, notably the simplicity of calculation procedures.